This invention relates to a process for preparing long chain alkyl aromatic compounds by alkylating an aromatic compound with a relatively long chain alkylating agent employing a particular class of Lewis-acid promoted zeolites as alkylation catalysts.
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties. Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline silicates. These silicates can be described as a rigid three-dimensional framework of SiO.sub.4 and Periodic Table Group IIIA element oxide, e.g., AlO.sub.4, in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total Group IIIA element, e.g., aluminum, and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing the Group IIIA element, e.g., aluminum, is balanced by the inclusion in the crystal of a cation, e.g., an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of the Group IIA element, e.g., aluminum, to the number of various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given silicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. Many of these zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite Z (U.S. Pat. No. 2,882,243); zeolite X (U.S. Pat. No. 2,882,244); zeolite Y (U.S. Pat. No. 3,130,007); zeolite ZK-5 (U.S. Pat. No. 3,247,195); zeolite ZK-4 (U.S. Pat. No. 3,314,752); zeolite ZSM-5 (U.S. Pat. No. 3,702,886); zeolite ZSM-11 (U.S. Pat. No. 3,709,979); zeolite ZSM-12 (U.S. Pat. No. 3,832,449); zeolite ZSM-20 (U.S. Pat. No. 3,972,983); zeolite ZSM-35 (U.S. Pat. No. 4,016,245); and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.
The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of a given zeolite is often variable. For example, zeolite X can be synthesized with SiO.sub.2 /Al.sub.2 O.sub.3 ratios of from 2 to 3; zeolite Y, from 3 to about 6. In some zeolites, the upper limit of the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is unbounded. ZSM-5 is one such example wherein the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is at least 5 and up to the limits of present analytical measurement techniques. U.S. Pat. No. 3,941,871 (U.S. Pat. No. Re. 29,948) discloses a porous crystalline silicate made from a reaction mixture containing no deliberately added alumina in the recipe and exhibiting the X-ray diffraction pattern characteristic of ZSM-5. U.S. Pat. Nos. 4,061,724, 4,073,865 and 4,104,294 describe crystalline silicates of varying alumina and metal content.
The alkylation of aromatic hydrocarbon with olefin employing a Lewis acid or Friedel-Crafts catalyst, e.g., AlCl.sub.3, BF.sub.3, HF, etc., to provide alkyl aromatic compounds is known in the art. Thus, for example, the alkylation processes described in U.S. Pat. Nos. 2,939,890 and 3,131,230 utilize a catalyst composition containing BF.sub.3 and a BF.sub.3 -modified substantially anhydrous inorganic oxide such as anhydrous gamma-alumina. U.S. Pat. No. 3,173,965 discloses the alkylation of benzene with olefin in the presence of a Friedel-Crafts catalyst, e.g., AlCl.sub.3, AlBr.sub.3, FeCl.sub.3, SnCl.sub.4, BF.sub.3, ZnCl.sub.2, HF, H.sub.2 SO.sub.4, P.sub.2 O.sub.5 and H.sub.3 PO.sub.4, to provide a polyalkylated benzene product of relatively high viscosity index (V.I.), i.e., from 90 to 145, which is useful as a lubricant. According to U.S. Pat. No. 4,035,308, excess benzene is alkylated with decene dimer in the presence of BF.sub.3 -promoted anhydrous AlCl.sub.3 to provide a monoalkyl benzene product useful as a lubricant or power transmission fluid. U.S. Pat. No. 4,148,834 describes a two-step alkylation process for preparing di-long chain alkyl aromatic compounds, useful as lubricants, in which aromatic hydrocarbon is alkylated with linear monoolefin in the presence of HF catalyst in a first step and aluminum chloride or aluminum bromide catalyst in a second step.
U.S. Pat. No. 4,691,068 discloses the preparation of long chain monoalkyl aromatics, useful in producing detergents, employing a Friedel-Crafts catalyst, e.g., AlCl.sub.3 -HCl, and featuring the recycle of a heavy boiling product fraction to the alkylation reaction.
With the aim of moving away from the use of strong acids as alkylation catalysts, the use of zeolites such as those referred to above has been investigated for the catalysis of aromatic hydrocarbon alkylation. Thus, the alkylation of aromatic hydrocarbons with an olefin in the presence of a zeolite having uniform pore openings of from about 6 to about 15 Angstrom units is described in U.S. Pat. No. 2,904,607. U.S. Pat. No. 3,251,897 describes the alkylation of aromatic hydrocarbons in the presence of X- or Y-type zeolites, specifically such type zeolites wherein the cation is a rare earth metal species and/or hydrogen. U.S. Pat. Nos. 3,751,504 and 3,751,506 describe the vapor phase alkylation of aromatic hydrocarbons with olefins, e.g., benzene with ethylene, in the presence of a ZSM-5 type zeolite catalyst. U.S. Pat. Nos. 3,631,120 and 3,641,177, describe a liquid phase process for the alkylation of aromatic hydrocarbons with olefins in the presence of certain zeolites. U.S. Pat. Nos. 4,301,316 and 4,301,317 disclose the use of such zeolites as ZSM-4, ZSM-20, ZSM-38, mazzite, Linde Type L and zeolite Beta to catalyze the alkylation of benzene with relatively long chain olefins to produce long chain alkylbenzenes.
U.S. Pat. No. 4,384,161 describes alkylation of isoparaffins with olefins over a Lewis acid-promoted large pore zeolite such as zeolite Beta, ZSM-4 and ZSM-20 to yield product having a large proportion of highly branched alkylates for blending into gasoline.